U.S. patent number 4,719,976 [Application Number 06/825,095] was granted by the patent office on 1988-01-19 for hammer drill.
This patent grant is currently assigned to Robert Bosch GmbH. Invention is credited to Manfred Bleicher, Ulrich Bohne, Karl Wanner.
United States Patent |
4,719,976 |
Bleicher , et al. |
January 19, 1988 |
Hammer drill
Abstract
A hammer drill is provided with a clutch whose movable part is
firmly connected to an axially displaceable drum which supports a
wobbling disc driving a percussive mechanism for striking a work
tool. The axially fixed clutch part is rotated by driving motor and
is backed-up by a housing of the drill. Retroacting forces from the
percussive mechanism are transferred via the drum onto the movable
clutch part so that the engagement of the clutch is reinforced at
the moment when the compression generated by percussive mechanism
is maximum. When pressure applied on work tool is relieved, a
separating spring disengages the clutch and braking surfaces on the
drum limit its axial displacement and brake the rotation of the
wobbling disc.
Inventors: |
Bleicher; Manfred
(Leinfelden-Echterdingen, DE), Bohne; Ulrich
(Kohlberg, DE), Wanner; Karl
(Leinfelden-Echterdingen, DE) |
Assignee: |
Robert Bosch GmbH (Stuttgart,
DE)
|
Family
ID: |
6263570 |
Appl.
No.: |
06/825,095 |
Filed: |
January 31, 1986 |
Foreign Application Priority Data
|
|
|
|
|
Feb 26, 1985 [DE] |
|
|
3506695 |
|
Current U.S.
Class: |
173/109; 173/201;
173/205; 74/60 |
Current CPC
Class: |
B25D
16/003 (20130101); Y10T 74/18336 (20150115) |
Current International
Class: |
B25D
16/00 (20060101); B25D 011/10 () |
Field of
Search: |
;173/47,48,109,116,122,123 ;74/57,60 ;192/66,99S |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bell; Paul A.
Assistant Examiner: Wolfe; James L.
Attorney, Agent or Firm: Striker; Michael J.
Claims
What is claimed as new and desired to be protected by Letters
Patent is set forth in the appended claims.
1. A hammer drill having a housing and, within the housing, means
for guiding work tool, a driving motor coupled by a gear train and
a motion converting wobble disc means to a percussive mechanism
acting via a resilient buffer on an axially reciprocating striking
member whose energy is transferred to a work tool inserted in said
guiding means, comprising a clutch arranged in said gear train to
transmit torque from said driving motor to said wobble disc means
when brought in engaged condition in response to a contact pressure
of the work tool against a workpiece, the clutch including an
axially movable clutch part arranged for joint rotation with the
wobble disc means and an axially fixed clutch part driven by said
gear train and being backed up by said housing, said means for
guiding a work tool being supported for axial movement relative to
said housing; and said axially movable clutch part being brought
into engagement with said axially fixed clutch part by the action
of said percussive mechanism transmitting back forces via said
wobble disc means when the work tool is pressed against a
workpiece.
2. A hammer drill as defined in claim 1, wherein the axially fixed
clutch part is rotatably supported in a fixed position in said
housing.
3. A hammer drill as defined in claim 2, wherein said gear train
includes an intermediate shaft supported for rotation in said
housing, a driving gear secured at one end to said shaft and
engaging a pinion of said driving motor and said axially fixed
clutch part being rigidly connected to said intermediate shaft.
4. A hammer drill as defined in claim 3, wherein said axially fixed
clutch part is integrally connected to a side of said driving
gear.
5. A hammer drill as defined in claim 4, wherein said wobble disc
means includes a wobble disc supported for rotation on a drum which
is axially displaceable on said intermediate shaft and said axially
movable clutch part being detachably connected to said drum.
6. A hammer drill as defined in claim 4, wherein said wobble disc
means includes a wobble disc supported for rotation on a drum which
is supported for rotation and axial displacement on said
intermediate shaft and said axially movable clutch part being
integrally connected to said drum.
7. A hammer drill as defined in claim 6, wherein said drum is
supported for rotation and for limited axial displacement on a
needle bearing provided on said intermediate shaft.
8. A hammer drill as defined in claim 6, wherein the axial
displacement of said movable clutch part and of said drum is
limited such that said clutch is brought in its engaged condition
by the retroacting force of said percussive mechanism.
9. A hammer drill as defined in claim 8, wherein the clutch is in
the form of a frictional conical clutch.
10. A hammer drill as defined in claim 9, wherein said axially
movable clutch part has a conical inner wall cooperating with a
conical outer surface of said axially fixed clutch part.
11. A hammer drill as defined in claim 10, wherein a side of the
driving gear attached to said intermediate shaft is formed with a
frusto-conical hub converging toward said axially movable clutch
part and being provided on its jacket with said outer conical
surface of said axially fixed clutch part.
12. A hammer drill as defined in claim 11; further comprising a
separating spring for disengaging said movable clutch part from
said fixed clutch part.
13. A hammer drill as defined in claim 12, wherein said separating
spring is a conical spring.
14. A hammer drill as defined in claim 12, wherein said separation
spring is a plate spring coaxially arranged between said movable
and fixed clutch parts.
15. A hammer drill as defined in claim 14, wherein said axially
movable clutch part is provided with a stop surface cooperating
with an opposite surface provided on the housing to limit the axial
displacement of the movable clutch part in disengaging direction
and to stop rotation of said drum.
16. A hammer drill having a housing and, within the housing, means
for guiding a work tool, a driving motor coupled by a gear train
and a motion converting wobble disc means to a percussive mechanism
acting via a resilient buffer on an axially reciprocating striking
member whose energy is transferred to a work tool inserted in said
guidnig means, comprising a clutch arranged in said gear train to
transmit torque from said driving motor to said wobble disc means
when brought in engaged condition in response to a contact pressure
on the work tool against a workpiece, the clutch including an
axially movable clutch part arranged for joint rotation with the
wobble disc means and an axially fixed clutch part driven by said
gear train and being backed up by said housing, said means for
guiding a work tool being supported for axial movement relative to
said housing and said axially movable clutch part being brought
into engagement with said axially fixed clutch part by the action
of said percussive mechanism transmitting back forces via said
wobble disc means when the work tool is pressed against a
workpiece; said axially fixed clutch part being rotatably supported
in a fixed position in said housing; said gear train including an
intermediate shaft supported for rotation in said housing, a
driving gear secured at one end to said shaft and engaging a pinion
of said driving motor, said axially fixed clutch part being rigidly
connected to said intermediate shaft; said axially fixed clutch
part being integrally connected to a side of said driving gear;
said wobble disc means including a wobble disc supported for
rotaton on a drum which is supported for rotation and axial
displacement on said intermediate shaft; said axially movable
clutch part being integrally connected to said drum; the axial
displacement of said movable clutch part and of said drum being
such that said clutch is brought in its engaged condition by the
retroacting force of said percussive mechanism; said clutch being
in the form of a frictional conical clutch; said axially movable
clutch part having a conical inner wall cooperating with a conical
outer surface of said axially fixed clutch part; a side of the
driving gear attached to said intermediate shaft being formed with
a frusto-conical hub converging toward said axially movable clutch
part and being provided on its jacket with said outer conical
surface of said axially fixed clutch part; a separating spring for
disengaging said movable clutch part from said fixed clutch part;
said separting spring being a plate spring coaxially arranged
between said movable and fixed clutch parts; said axially movable
clutch part being provided with a stop surface cooperating with an
opposite surface provided on the housing to limit the axial
displacement of the movable clutch part in disengaging direction
and to stop rotation of said drum; and further comprisng a power
transmitting member in the form of a fork-like lever anchored in
said housing and extending between said axially displaceable
guiding means and said drum, said lever acting on said drum in the
engaging direction of said movable clutch part against the force of
the separating spring and the ratio of distancs of the contact
point of the lever with the drum to the contact point with the
housing and with said guiding means determining the amplification
of the transmitted power holding the clutch in its engaged position
when the hammer drill is in operaton.
17. A hammer drill as defined in claim 16, wherein said separating
spring is arranged between and supported on said clutch parts.
18. A hammer drill as defined in claim 16, wherein said separating
spring is arranged outside said coupling to act on said movable
clutch part in disengaging direction via an intermediate
member.
19. A hammer drill as defined in claim 18, wherein said power
transmitting lever is provided with a hook-shaped catch engaging a
flange in said drum, and said separating spring acting on said
lever to move by means of said catch the drum in the disengaging
direction.
20. A hammer drill as defined in claim 19, wherein said lever is
pivotably supported on said housing at a pivot point which is
spaced apart from said hook-shaped catch.
21. A hammer drill as defined in claim 20, wherein the free end of
said lever engages the percussive mechanism and said separating
spring being arranged between the housing and said free end of the
lever to act in the striking direction of the percussive mechanism
and upon relief of the retroacting pressure the separating spring
pivots the lever into its initial position in which the hook-shaped
catch displaces the drum and hence the movable clutch into a
disengaged position and a part of the lever acts as a stop surface
for limiting the axial displacement of the drum and for braking its
rotation.
Description
BACKGROUND OF THE INVENTION
The present invention relates in general to a hammer drill and in
particular to a hammer drill of the type which includes a housing
and, within the housing, means for guiding a work tool, a driving
motor coupled by a gear train and a motion converting wobble disc
to a reciprocating driving member acting via a resilient buffer,
preferably an air cushion, on an axially reciprocating striking
member whose energy is transferred to a work tool inserted in the
guiding means.
From U.S. Pat. Nos. 4,280,359; 4,537,264 a hammer drill of this
kind is known in which the drum supporting the wobbling disc is
supported for rotation on an intermediate shaft which in turn is
supported in the housing of the hammer drill. In the gear train
between the intermediate shaft and the drum of the wobbling disc
there is provided a frictional coupling which is normally
disengaged by means of a spring so that the drum with the wobbling
disc is not driven via the intermediate shaft: only after pressing
the work tool on a processed workpiece a corresponding reaction
force becomes effective in counteracting the biasing force of the
coupling spring and the coupling is brought in its engaged
condition, thus transferring torque from the intermediate shaft to
the drum and the wobbling disc and hence to the percussive
mechanism of the hammer drill. The moving part of the coupling in
this known embodiment consists of a conical shaft end which is
fixedly connected to the rotary intermediate shaft. The other
coupling part is formed by the drum provided with the wobbling
disc, the drum being firmly stayed in axial direction relative to
the housing. The effect of the coupling between the driving motor
and the driving member of the percussive mechanism depends on
pressure exerted by operator against a workpiece. If the pressing
force is sufficiently large, the intermediate shaft which acts as a
carrier of the movable coupling part is displaced axially against
the force of a separation spring into an inner cone of the axially
fixed part of the coupling on the drum supporting the wobbling disc
and consequently the drum with the wobbling disc and the percussive
mechanism are activated. Due to this prior art design the operation
of the hammer drill is rendered difficult. Also a reliable
engagement of the driving member of the percussive mechanism
depends on individually different, nonreproducible circumstances,
such as for example different pressing forces applied on the hammer
drill by different users. Moreover, due to the support of the drum
carrying the wobbling disc, the reaction forces from the percussive
mechanism taken up by the housing act in the direction of
disengagement of the coupling. Hence, precisely at the point of
greatest compression when the percussive mechanism is supposed to
apply the largest compressing force and consequently in the range
of the drum with wobbling disc to apply the largest torque to the
coupling, the reaction force acting in the direction of the
disengagement of the coupling has its peak value. For this reason,
the operator has to apply relatively large pressing forces on the
hammer drill.
SUMMARY OF THE INVENTION
It is therefore a general object of the present invention to
overcome the above mentioned disadvantages.
In particular, it is an object of this invention to provide such an
improved hammer drill which in comparison with prior art has the
advantage in an extremely small pressing force required from the
user during the hammer drilling operation whereby the actual
locking force acting on the coupling is markedly larger than in
conventional hammer drills.
In keeping with these objects and others which will become apparent
hereafter, one feature of this invention resides, in a hammer drill
of the before described kind, in a combination in which the movable
part of the coupling which performs the engaging and disengaging
movements is rigidly connected to the wobbling disc for a joint
rotation therewith and the other coupling part is firmly supported
in the housing of the hammer drill, and means for pressing the
movable coupling part together with the wobbling disc, by the
action of the percussive mechanism, against the axially fixed other
coupling part which takes up the percussive reaction forces.
Due to the firm connection of the engageable and disengageable
coupling part with the rotary wobbling disc while the other
coupling part is fixedly supported on the housing to take up the
reaction forces from the percussive mechanism, the return strokes
of the percussive mechanism acting on the wobbling disc produce an
amplification of the pressing force on the two coupling parts. The
locking connection of the two coupling parts is thereby increased
by the compressing force of the percussive mechanism. Consequently,
when a largest force is needed by the percussive mechanism for
driving the piston as is the case at the moment of the greatest
compression of the gaseous spring or air cushion of the percussive
mechanism, the torque transmitted by the coupling is also at its
peak due to the kickback of the percussion. Therefore, the operator
experiences a substantially simpler manipulation and the pressing
forces needed to be applied against a workpiece are substantially
smaller. The resulting hammer drill is lightweight, economic to
manufacture, compact in design and vibration free.
In a preferred embodiment of this invention, there is provided a
separation spring between the two coupling parts, the spring acting
in the disengaging direction. The separating spring is dimensioned
such that even if the hammer drill is turned upwards any resetting
forces resulting from the own weight of respective parts of the
percussive mechanism and of the drive, are sufficiently
counteracted and the coupling is kept in disengaged condition.
In another preferred embodiment of this invention the drum which is
integral with the movable coupling part is provided with firm
braking or stop surfaces which in the disengaged condition of the
coupling are pressed by the separating spring against opposite stop
surfaces mounted on the housing to stop rotation of the drum and of
the movable coupling part. This provision also contributes to a
problem free non-load behavior of the hammer drill and to a further
reduction of possible vibrations.
In still another advantageous embodiment of this invention the
means for transferring retroactive forces from the percussive
mechanism are in the form of a fork like lever whose forked end is
acted upon by the pressure applied by the work tool against the
workpiece. This pressure is transferred in the same direction at an
intermediate point onto the drum carrying the movable coupling
part. The opposite end of the lever is fulcrummed in the housing
and the ratio of distances of the intermediate point to the ends of
the lever determines the amplification of the transmitted power. In
a modification, the lever acts also with an amplified power on the
drum in disengaging direction so as to facilitate the disengagement
of the coupling parts. In the latter case, the separating spring
acts on the fork-like end of the lever at a distance from its
contact point with the drum carrying the movable coupling part and
the lever is equipped with a catch engaging a collar or flange on
the corresponding end of the drum opposite the coupling. In this
manner, the force of the separating spring is amplified and the
lever easily disengages the two coupling parts and simultaneously
the braking effect of the stop surfaces is improved and the
rotation of the drum is effectively stopped. The separating spring
in this modification is spaced apart from rotating parts and is not
subject to any wear.
The novel features which are considered as characteristic for the
invention are set forth in particular in the appended claims. The
invention itself, however, both as to its construction and its
method of operation, together with additional objects and
advantages thereof, will be best understood from the following
description of specific embodiments when read in connection with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 a side view partly in section of a schematically illustrat
hammer drill according to a first embodiment of this invention;
and
FIG. 2 is a sectional side view of a driving part of the hammer
drill of FIG. 1 having a modified power transferring member between
the percussive mechanism and a movable part of a coupling.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hammer drill illustrated in FIG. 1 has a housing 1 in which an
electric motor 2, a gear train 3 and a percussive mechanism 4 are
accommodated. Axis 4' of the percussive mechanism 4 extends
parallel to the axis of rotation of the electric motor 2. Rear part
of housing 1 transits in a handle 5 in which a power switch
controlled by a pushbutton 6 is installed, through which the
electric motor 2 is activated. The lower end of the handle 5 is
provided with an elastic sleeve (nonillustrated) through which a
power supply cable is led in. The front end of the housing remote
from the hand grip 5 is provided with a work tool holder 8 serving
for receiving work tools, for example a drill bit 9.
The electric motor 2 has a driving shaft 10 which at both ends
thereof is rotatably supported in housing 1 by ball bearings of
which ball bearing 11 is shown in the drawing. The end of driving
shaft 10 projecting through ball bearing 11 is provided With a
pinion 12 which meshes with a gear 13. Preferably, the gear 13 and
the motor pinion 12 are helical gears. The gear 13 is fixedly
connected for example by pressing to a rotary intermediate shaft
14. The end of intermediate shaft 14 adjoining the gear 13 is
supported for rotation in a ball bearing 19 whose outer race 20 is
firmly connected to a partition 51 of housing 1 whereas the inner
race 21 of bearing 19 is attached to a stepped down end portion of
the intermediate shaft. The intermediate shaft passes through an
axial bore 15 of a drum 16. The diameter of the bore 15 is larger
than the diameter of the intermediate shaft and the drum 16 is
rotatably supported on the intermediate shaft by means of a needle
cage 17. The needle cage 17 is dimensioned such that the drum 16 is
slightly shiftable in axial direction relative to the intermediate
shaft 14. An end portion of the intermediate shaft 14 remote from
the ball bearing 19 is supported for rotation in a needle bearing
18 whose outer race is secured to a partition of housing 1. The
free end of the intermediate shaft projecting from the needle
bearing 18 is fixedly connected to a pinion 35 whose function will
be explained below.
The jacket of drum 16 is formed with a bearing groove 23 whose
plane is inclined relative to the axis of rotation of the
intermediate shaft 14. The bearing groove 23 represents an inner
raceway for balls 24 of ball bearing 25. Outer race of ball bearing
25 forms a wobbling disc 26 provided with a finger 27 which is in
driving contact with the percussive mechanism 4.
The percussive mechanism 4 is arranged within a guiding tube 28
which is rotatably supported in housing 1. In this embodiment the
guiding tube 28 is firmly connected to the inner end of a tubular
work tool holder 8. Within the guiding tube 28 there is arranged an
axially reciprocating piston 29 which is in tight sliding contac
with the inner wall of the guiding tube and acts as a driving
member of the percussive mechanism. The end portion of piston 29
remote from tool holder 8 has a fork-shaped configuration and
supports a pivot pin 31. An intermediate part of the pivot pin is
formed with a transverse bore 82 which is in loose engagement with
the finger 27 of the wobbling disc. In this manner, the finger 27
easily moves in its axial direction through the transverse bore 32.
Within the hollow piston 29 a cylindrical striking member 33 is
guided in sealing contact with the inner wall of the piston to act
via an anvil 34 against the rear end of the work tool 9.
The above mentioned pinion 35 secured to the free end of the
intermediate shaft 14 side by side with the needle bearing 18 is in
mesh with a gear 36 which is shiftably supported on the jacket of
guiding tube 28 and is free to rotate about the center axis of the
latter. The gear 36 is biased by a pressure spring 46 against a
flange 50 formed near the rear end of the guiding tube 28. The
facing end surfaces of the gear 36 and of the flange 50 are formed
with radial projections 37 and 38, respectively. The projections
engage each other and due to the biasing effect of pressure spring
46 serve as an overload coupling. The driving gear 13 pressed on
the opposite end of the intermediate shaft is provided with a
frusto-conical hub 22 whose conical outer surface 41 converges in
axial direction toward the drum 16. The juxtaposed end of drum 16
is provided with a frusto-conical sleeve 39 whose inner conical
wall 40 matches the outer conical surface of the conical hub 22.
The surface 40 and 41 form together a coupling or clutch which in
engaged condition connects for joint rotation the drum 16 with the
driving gear 13, thus causing a joint rotation of the intermediate
shaft 14 with the drum 16. The engagement of the conical coupling
40/41 takes place by the action of the guiding tube 28 which upon
pressing the drill bit 9 against a processed workpiece is shifted
in axial direction rearward relative to housing 1.
During the axial displacement of the guiding tube, the rear end
face of drill bit 9 presses via the anvil 34, an abutment ring 43
and a clip ring 42 the guiding tube 28 rearwards. Accordingly,
pressure applied against the drill bit 9 causes an axial shift of
the tool holder 8 together with guiding tube 28 into the housing 1.
During this relative shift, the flange 50 on the jacket of guiding
tube 28 presses via an axial bearing 48 and an annular disc 49
against the fork-like end 44 of the power transferring lever 45. Of
the two prongs of the fork-like end 44 of the lever embracing the
guiding tube 28, only one prong or shank is illustrated in FIG. 1.
The other end 54 of lever 45 has also a fork-like shape and
embraces the intermediate shaft 14. At the level of the center axis
of the intermediate shaft 14 the lever 45 is provided at both
shanks of the fork-like end 54 with projections 55 slidably
engaging a disc 56 which in turn is connected via an axial bearing
57 to the corresponding end face of the drum 16. The free ends of
the fork-like part 54 of lever 45 are held in a recess 58 in
housing 1. An eccentric pin 59 is rotatably supported in proximity
to the recess 58 and is adjusted to engage a surface 61 at the
opposite side of fork-like portion 54 of lever 45 below the contact
point between the projection 55 and the disc 56. The eccentric pin
59 is adjusted into a position in which the projections 55 are
brought into contact with the disc 56 while the oppositely directed
projections 44' at the opposite end of lever 45 are in contact with
the disc 49 surrounding the rear end of guiding tube 28.
When in pressing a work tool 9 in the hammer drill against a
processed workpiece, the guiding tube 28 is shifted into housing 1
and the pressure is transmitted via flange 50, axial bearing 48
onto the annular disc 49 which in turn rotates the upper end 44 of
lever 45 about the contact point with the eccentric pin 59. During
this pivotal movement, projections 55 axially displace via the
annular disc 56 and axial bearing 57 the drum 16 on the needle cage
and consequently the sleeve 39 with the inner conical surface 40
engages the outer conical surface 41 on the driving gear 13 and the
conical clutch 40/41 is brought into its engaged condition. The
lever 45 is made of a resilient material which is dimensioned such
that upon a further increase of pressure against the work tool a
further rearward displacement of the guiding tube 28 into the
housing takes place nevertheless force applied via the projection
55 and drum 16 on the conical coupling or clutch 40/41 does not
exceed a predetermined value.
The effect of pressing force an operator applies on the hammer
drill is amplified during its transmission by lever 45 on the
conical coupling 40/41. The power amplification depends on the
ratio of the distance of projections 55 from the points of contact
of the lever end 44 with the disc 49 to the distance of the
projection 55 from the pivot point at the opposite lever end 54. By
adjusting the position of the eccentric pin 59 it is made possible
to compensate in simple manner manufacturing tolerances.
It will be seen from FIG. 1, the movable part of the coupling is
the inner conical wall 40 of sleeve 39 which is an integral
component part of drum 16 carrying the wobbling disc 26.
Consequently, the movable coupling part is pressed by the action of
the percussive mechanism 4 against the axially fixed coupling part
constituted by the outer conical surface 41 on hub 22 formed on a
face of driving gear 13 which in turn is rigidly connected to the
rotary intermediate shaft 14 which by means of ball bearing 19 is
supported on housing 1. Since the drum 16 is within narrow limits
axially shiftable on the intermediate shaft then during drilling
operation of the hammer drill, reaction forces resulting from
strikes against piston 29 and transmitted to wobbling disc 26 are
taken up by the drum and the latter is shifted axially toward the
hub 22 whereby the frictional engagement between the two coupling
parts 40/41 is still increased. In this manner, the transmission of
the driving torque through the conical coupling 40/41 is improved.
Accordingly, at the time point when a maximum force is to be
transmitted to percussive mechanism 4 for driving the piston 29 and
with the maximum compression between the piston 29 and the striking
member 33 then the frictional engagement of the coupling parts and
the transmitted torque are also maximal. The compressing force
generated by the percussive mechanism 4 reacts through piston 29,
pivot pin 31, finger 27, wobbling disc 26, bolts 24, drum 16,
sleeve 39 and the inner conical wall 40 on the outer conical
surface 41 of the hub 22 and is taken up via driving gear 13 and
ball bearing 19 by housing 1. This back-up of the reaction force by
the housing occurs exactly at the moment when the largest
frictional engagement of the coupling and consequently the largest
driving moment is required for a slipless rotary driving of drum 16
together with wobbling disc 26. The movable coupling part 39, 40
which is an integral component part of drum 16 is thus always
compressed in counter direction to generated strikes and is shifted
on intermediate shaft 14 to the right in FIG. 1 to reinforce the
engagement with the axially fixed coupling part 22, 41.
It will be understood that in a nonillustrated modification of this
embodiment, the coupling parts can be kinematically reversed so
that the outer conical surface is provided on the drum whereas the
inner conical wall is formed on the corresponding side of driving
gear 13.
A separating spring 47 is arranged between the two coupling parts
namely between the sleeve 39 and the hub 22. In the embodiment of
FIG. 1, the separation spring is in the form of a plate spring
whose inner annular part is supported on hub 22 and whose outer
annular part is supported on a flange within the sleeve 39. In this
case, the separation spring 47 immediately acts on drum 16
supporting the movable coupling part. The separating spring can be
also in the form of a pressure spring which exerts an axial
pressure between the two coupling parts 40/41 to urge the coupling
into its disengaged condition.
The illustration in FIG. 1 shows the coupling 40/41 in its engaged
position when the separating force of spring 47 is exceeded.
Sleeve 39 on drum 16 is further provided on its outer surface with
a rigid braking member in the form of a collar 62 cooperating with
a stationary braking ring 63 secured to housing
The clearance between the opposite braking surfaces is dimensioned
such that in disengaged of coupling 40/41 the rotation of drum 16
is immediately stopped and thus any vibrations are prevented.
Hammer drill illustrated in FIG. 1 is in an operational condition
in which work tool 9 is pressed on a nonillustrated workpiece
whereby power transmitting lever 45 is pivoted at contact point
with eccentric pin 59 into a position in which projection 55
displaces drum 16 to the right and consequently the movable
coupling part with inner conical wall 40 is pressed against the
rotating but axial fixed outer conical surface 41 on hub 22 and
coupling is in its engaged condition. The force of separating
spring 47 is thereby overcome.
When back pressure from work tool 9 decreases, the separating
spring 47 shifts drum 16 with the movable coupling part 39, 40 away
from the axially fixed coupling part 22, 41 and the coupling 40/41
is disengaged. This axial movement is stopped after flange 62 on
the sleeve 39 abuts against the stationary stop ring 63 of the
housing. The engaging surfaces of flange 62 and ring 63, as
mentioned before act as braking surfaces which stop the rotation of
drum 16 and consequently the percussive mechanism 4. However, the
driving mechanism consisting of motor pinion 12, driving gear 13,
hub 22, intermediate shaft 14, shaft pinion 35, gear 36, overload
coupling 37/38, flange 50 and guiding tube 28 with tool holder 8,
keep running.
By virtue of the amplification of the compression force exerted by
percussive mechanism 4 against the coupling and hence the increase
of transmitted torque from driving mechanism, the operation comfort
of the hammer drill is substantially increased because the operator
need not press hard against the workpiece.
When coupling 40/41 is in its disengaged condition, the separating
spring 47 in the form of a plate spring is practically exposed to
no wear because it contacts the interior of sleeve 39 and the hub
22 along a circular line only.
In operation when percussive mechanism 4 brings via the power
transmitted lever 45 the coupling 40/41 in its engaged condition
then by virtue of the amplification of the force exerted on drum 16
and determined by the ratio of lever arms between the ends 44, 54
and contact projections 55, the generated force is in all cases
sufficient for preventing axial displacement of the rotary drum 16
with wobbling disc 26 to the left on the intermediate shaft. In
other words, drum 16 is forced by the lower end 54 of lever 45 to
the right on the intermediate shaft so as to guarantee reliable
engagement of the coupling.
In the embodiment of this invention illustrated in FIG. 2, the last
two digits in reference numerals correspond to reference numerals
in the preceding example designating like component parts. The
nonillustrated parts of the hammer drill are of the same design as
in FIG. 1.
The arrangement of the control mechanism for the coupling shown in
FIG. 2 differs from the preceding example by a different location
of separating spring 147 which is no longer coaxial with the drum
116 and hub 122 but is situated outside the coupling 140/141. The
separating spring 147 in this embodiment is a cylindrical helical
spring acting on the upper fork-like end 144 of the power
transmitting lever 145. The opposite end of separating spring 147
is supported on a housing partition 101. The axis of separating
spring 147 coincides with the center axis of percussive mechanism
104. Preferably, each shank 144 of fork-like lever 145 is loaded by
an assigned separating spring.
The lever 145, similarly as in the preceding example, is provided
with projections 155 acting via annular disc 156 and axial bearing
157 against an end side of drum 116. An intermediate part of lever
145 is provided with a hook-shaped catch 164 which can be stamped
in the material of the lever and shaped by bending. The hook-shaped
end portion of the catch 164 is directed at right angles opposite
the inner side of a flange 162 formed on the end of drum 16 remote
from ball bearing 119. The lower end of lever 146 is pivotably
supported on a pin 165 secured to housing 101.
When the work tool is pressed on workpiece, then the corresponding
back pressure is transmitted via disc 149 on the fork-like end 144
of lever 145. Consequently the lever is pivoted about the pivot pin
165 against the biasing force of separating spring 147. Projections
155 on the fork-like lower end 154 of the lever exert pressure via
disc 156 and axial bearing 157 on the flange 162 of drum 116 and
the latter is shifted axially on intermediate shaft 114 to the
right until the inner conical wall 140 engages the outer conical
surface 141 on hub 122. At this moment, the coupling starts
transmitting driving torque and the drum 116 starts rotating and
its wobbling disc 127 sets percussive mechanism 104 in
reciprocating motion. Similarly as in the preceding example,
reaction forces generated in percussive mechanism 104 are taken up
via drum 116, clutch 140/141, hub 122 and ball bearing 119 on
housing 101. As a result, a largest frictional engagement is
automatically developed in coupling 140/141 when a maximum
compression between the piston and striking member of percussive
mechanism 104 is present, and a maximum driving force is applied to
the piston.
When the back pressure from work tool drops, separating spring 147
is relieved and lever 145 is pivoted about pivot pin 165 into its
starting position in which the upper fork-like end 144 is displaced
to the left. During this return movement of lever 145 the catch 164
engages the flange 162 and moves the drum 116 on the intermediate
shaft 114 to the left, thus disengaging the coupling 140/141. When
the coupling is disengaged, the outer surface of flange 162 is
clamped with the projection 155 of lever 145 whereupon the axial
movement of drum 116 is stopped and simultaneously its rotation is
braked and the percussive mechanism 104 stands still.
As mentioned before, in the second embodiment the separating spring
147 is not rotated by the coupling and therefore no problems with
the wear of the spring occur.
In the embodiment of FIG. 2, movable coupling part 139, 140 is not
an integral part of the drum 16 but forms a separate element which
is releasably connected to the drum 116, for example by a screw
connection 139. In a nonillustrated modification of the embodiment
of FIG. 1, the movable coupling part 39, 40 is a separate element
which is positively connected by coupling members to drum 16. The
coupling members can be for example in the form of coupling face
teeth on the movable coupling part 39, 40 and on the end face of
drum 16 which engage in axial direction with each other. The
coupling members can be also in the form of radial teeth. It will
be understood also that needle cage 17 which in the first
embodiment serves as a bearing of drum 16 on the intermediate shaft
can be dispensed with whereby drum 116 is directly supported on the
intermediate shaft 14 for rotation and limited axial displacement
on the latter.
In a further nonillustrated embodiment, instead of a frictional
conical coupling there is provided a serrated coupling having
contact surfaces with interlocking teeth provided on facing ends of
drum 16 and of hub 22.
Instead of the air cushion between the piston 29 and the striking
member 33 acting as a resilient percussion transmitting medium, it
is also possible to employ a suitable spring.
While the invention has been illustrated and described as embodied
in specific examples of hammer drills, it is not intended to be
limited to the details shown, since various modifications and
structural changes may be made without departing in any way from
the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the
gist of the present invention that others can, by applying current
knowledge, readily adapt it for various applications without
omitting features that, from the standpoint of prior art, fairly
constitute essential characteristics of the generic or specific
aspects of this invention.
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